In 14.4 mL of ethanol was dissolved 10.0 g of 1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl}-3-azetidinol, followed by adding thereto 7.21 g of citric acid monohydrate, and the resulting mixture was heated at 50° C. to effect dissolution. To the resulting solution were added 35 mL of ethyl acetate and 5.6 mL of ethanol at 50° C., and stirred at 25° C. The reaction mixture was heated at 40° C., after which ethyl acetate (45 mL) was added dropwise thereto and the resulting mixture was stirred at 40° C. for 10 minutes and then at 10 to 20° C. for 1 hour. The crystals precipitated were collected by filtration to obtain 14.9 g of 1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl}-3-azetidinol citrate as colorless crystals.
